The coal that is used as fuel in electrical power generating plant equipped with a coal fired boiler turbine (hereafter simply referred to as a boiler) is classified as high-grade, medium grade, and low-grade, depending on the water content, coal rank, and the like.
Low-grade coal such as lignite and the like has high water content and low coal rank and low calorific value compared with high-grade coal, so in order to increase the combustion efficiency of the boiler, it is desirable that the coal be dried before being fed into the boiler.
Therefore, conventionally, the coal is dried by heating it using steam extracted from the boiler.
Also, it has been proposed that coal be heated and dried using combustion exhaust gas discharged from the outlet of an economizer and denitrification plant provided with the boiler (for example, see Patent Literature (PTL) 1).